Many techniques and procedures utilized in processing of diverse materials to obtain a particular end product also result in formation of a residue or by-product containing a high proportion of moisture. Such residue or by-products collectively termed "residual products" must be disposed of by methods or techniques that satisfy ecological standards and safety requirements. However, these residual products, because of their high moisture content, present disposal problems. Some residual products contain significant nutrient value so that they could be utilized as livestock, animal or poultry feed, or as agricultural fertilizer, but a high moisture content makes them difficult and costly to handle and utilize for those purposes and they are often simply disposed of as useless waste. For the same reason, a number of residual products that have potential as a source of energy can only be consigned to ultimate disposal such as in landfills. Generally, these residual products have a moisture content that is so proportionally high with respects to their solids, that they are not susceptible to economically feasible further processing to a state that permits their utilization.
One type of drying apparatus that has been utilized to effect drying of high moisture content materials is the, spray dryer. With this apparatus, the material to be dried is sprayed into a confined space through which heated air is caused to flow and effect vaporization of moisture from the material, leaving dry solids with the vaporized moisture being exhausted to the atmosphere. While a spray dryer can effect drying of some high moisture content materials, it accomplishes this drying with input of a relatively large amount of energy in the form of heat, and also mechanical, to cause a flow of large quantities of air at high velocity. Consequently, spray drying is a costly technique that cannot be economically justified for many residual products.
Another type of drying apparatus that has been utilized for drying of some high moisture content materials is the fluidized bed dryer. A fluidized bed dryer has a bedplate formed with apertures and on which the moist materials are placed. Heated air is caused to flow upwardly through the apertures and the material at volumes and velocities to effect fluidizing of the material with the objective of vaporization of the moisture. This technique does not work well with some materials as moist solids tend to agglomerate into large masses. The fluidizing heated air has difficulty in penetrating these agglomerated masses and, thus, the agglomerated material retains moisture in the interior of those masses and they are only dried on the outside. When these agglomerated masses of material are processed through the dryer, the retained moisture will move to their exterior, become sticky and tend to stick to subsequent processing apparatus as well as being an unacceptable, unusable product and which may cause the entire mass to spoil.
In particular, techniques previously used to effect drying of many organic materials have not found widespread use for economic reasons. The techniques for removal of the moisture have generally required input of substantial energy, primarily in the form of heat to effect vaporization of the moisture and enable it to be removed from the body of material. Organic materials, when processed by prior techniques, often exhibit a strong tendency to agglomerate into large masses that further hinders their drying.
Typical of the materials which are particularly adapted to the processing technique of this invention are the by-products that are produced from such processing operations in producing poultry products for human consumption and also in processing of milk products where a generally unutilizable material such as whey may be produced. Also, residue materials from slaughterhouse operations are often incapable of being readily used for production of food products, such as for cats and dogs, as they contain excessive amounts of moisture. Materials of that nature are difficult and uneconomical to process as the residual moisture content requires employment of preservation techniques such as refrigeration, in many cases, to maintain the product in a palatable state for consumption by animals. This problem is further compounded by the fact that materials containing high levels of moisture are normally only susceptible to storage for relatively short periods of time unless they are refrigerated or processed into storage containers that are suitable for preserving the contents. The requirement for utilization of such containers further compounds the problems of processing such materials as the containers represent a significant economic factor. Transportation of high moisture content materials is also economically disadvantageous.